Sintered polishing pad with regions of contrasting density

ABSTRACT

The invention provides a polishing pad comprising sintered particles of a thermoplastic resin, wherein a surface of the polishing pad intended to contact a substrate to be polished comprises (a) a non-patterned portion with a substantially uniform density and (b) a patterned portion with one or more densities that differ from the density of the non-patterned portion. The invention also provides a method for producing the polishing pad, a chemical-mechanical polishing apparatus comprising the polishing pad, and a method of polishing comprising contacting a substrate with the polishing pad.

FIELD OF THE INVENTION

[0001] This invention pertains to a polishing pad having regions ofcontrasting density.

BACKGROUND OF THE INVENTION

[0002] Chemical-mechanical polishing (“CMP”) processes are used in themanufacturing of microelectronic devices to form flat surfaces onsemiconductor wafers, field emission displays, and many othermicroelectronic substrates. For example, the manufacture ofsemiconductor devices generally involves the formation of variousprocess layers, selective removal or patterning of portions of thoselayers, and deposition of yet additional process layers above thesurface of a semiconducting substrate to form a semiconductor wafer. Theprocess layers can include, by way of example, insulation layers, gateoxide layers, conductive layers, and layers of metal or glass, etc. Itis generally desirable in certain steps of the wafer process that theuppermost surface of the process layers be planar, i.e., flat, for thedeposition of subsequent layers. CMP is used to planarize process layerswherein a deposited material, such as a conductive or insulatingmaterial, is polished to planarize the wafer for subsequent processsteps.

[0003] In a typical CMP process, a wafer is mounted upside down on acarrier in a CMP tool. A force pushes the carrier and the wafer downwardtoward a polishing pad. The carrier and the wafer are rotated above therotating polishing pad on the CMP tool's polishing table. A polishingcomposition (also referred to as a polishing slurry) generally isintroduced between the rotating wafer and the rotating polishing padduring the polishing process. The polishing composition typicallycontains a chemical that interacts with or dissolves portions of theuppermost wafer layer(s) and optionally an abrasive material thatphysically removes portions of the layer(s). The wafer and the polishingpad can be rotated in the same direction or in opposite directions,whichever is desirable for the particular polishing process beingcarried out. The carrier also can oscillate across the polishing pad onthe polishing table.

[0004] Polishing pads used in chemical-mechanical polishing processesare manufactured using both soft and rigid pad materials, which includepolymer-impregnated fabrics, microporous films, cellular polymer foams,non-porous polymer sheets, and sintered thermoplastic particles. A padcontaining a polyurethane resin impregnated into a polyester non-wovenfabric is illustrative of a polymer-impregnated fabric polishing pad.Microporous polishing pads include microporous urethane films coatedonto a base material, which is often an impregnated fabric pad. Thesepolishing pads are closed cell, porous films. Cellular polymer foampolishing pads contain a closed cell structure that is randomly anduniformly distributed in all three dimensions. Non-porous polymer sheetpolishing pads include a polishing surface made from solid polymersheets, which have no intrinsic ability to transport slurry particles(see, for example, U.S. Pat. No. 5,489,233). These solid polishing padsare externally modified with large and small grooves that are cut intothe surface of the pad purportedly to provide channels for the passageof slurry during chemical-mechanical polishing. A similar non-porouspolymer sheet polishing pad is disclosed in U.S. Pat. No. 6,203,407,wherein the polishing surface of the polishing pad comprises groovesthat are oriented in such a way that purportedly improves selectivity inthe chemical-mechanical polishing. Also in a similar fashion, U.S. Pat.Nos. 6,022,268, 6,217,434, and 6,287,185 disclose hydrophilic polishingpads with no intrinsic ability to absorb or transport slurry particles.The polishing surface purportedly has a random surface topographyincluding microaspersities that are 10 μm or less and formed bysolidifying the polishing surface and macro defects (or macrotexture)that are 25 μm or greater and formed by cutting. Sintered polishing padscomprising a porous open-celled structure can be prepared fromthermoplastic polymer resins. For example, U.S. Pat. Nos. 6,062,968 and6,126,532 disclose polishing pads with open-celled, microporoussubstrates, produced by sintering thermoplastic resins with a pelletsize of about 50 to about 200 mesh. The resulting polishing padspreferably have a void volume between 25 and 50% and a density of 0.7 to0.9 g/cm³. Similarly, U.S. Pat. Nos. 6,017,265, 6,106,754, and 6,231,434disclose polishing pads with uniform, continuously interconnected porestructures, produced by sintering thermoplastic polymers at highpressures in excess of 689.5 kPa (100 psi) in a mold having the desiredfinal pad dimensions.

[0005] In addition to groove patterns, polishing pads can have othersurface features to provide texture to the surface of the polishing pad.For example, U.S. Pat. No. 5,609,517 discloses a composite polishing padcomprising a support layer, nodes, and an upper layer, all withdifferent hardnesses. U.S. Pat. No. 5,944,583 discloses a compositepolishing pad having circumferential rings of alternatingcompressibility. U.S. Pat. No. 6,168,508 discloses a polishing padhaving a first polishing area with a first value of a physical property(e.g., hardness, specific gravity, compressibility, abrasiveness,height, etc.) and a second polishing area with a second value of thephysical property. U.S. Pat. No. 6,287,185 discloses a polishing padhaving a surface topography produced by a thermoforming process. Thesurface of the polishing pad is heated under pressure or stressresulting in the formation of surface features.

[0006] Although several of the above-described polishing pads aresuitable for their intended purpose, a need remains for an improvedpolishing pad that provides effective planarization, particularly insubstrate polishing by chemical-mechanical polishing. In addition, thereis a need for polishing pads having improved polishing efficiency,improved slurry flow across and within the polishing pad, improvedresistance to corrosive etchants, and/or improved polishing uniformity.Finally, there is a need for polishing pads that can be produced usingrelatively low cost methods and which require little or no conditioningprior to use.

[0007] The invention provides such a polishing pad. These and otheradvantages of the invention, as well as additional inventive features,will be apparent from the description of the invention provided herein.

BRIEF SUMMARY OF THE INVENTION

[0008] The invention provides a polishing pad comprising sinteredparticles of a thermoplastic resin, wherein a surface of the polishingpad intended to contact a substrate to be polished comprises (a) anon-patterned portion with a substantially uniform density and (b) apatterned portion with one or more densities that differ from thedensity of the non-patterned portion. The invention also provides amethod for producing the polishing pad comprising (i) providing apolishing pad with a first density comprising particles of athermoplastic resin, (ii) heating a portion of the polishing pad tocause the thermoplastic resin particles to flow, and (iii) cooling thepolishing pad, thereby causing the flowed thermoplastic resin particlesto solidify with a second density that is higher than the first densityand forming a polishing pad having a non-patterned portion with thefirst density and a patterned portion with one or more densities thatdiffer from the density of the non-patterned portion. The inventionfurther provides a chemical-mechanical polishing apparatus comprisingthe polishing pad, a platen in contact with the polishing pad, and acarrier that holds a substrate to be polished. The invention furtherprovides a method of polishing comprising (i) contacting a substratewith the polishing pad and a polishing composition and (ii) moving thesubstrate relative to the polishing pad to abrade at least a portion ofthe substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is an illustration of a polishing pad contacting a heatedpattered roller having a plurality of raised pins mounted onto thecylinder of the roller.

[0010]FIG. 2 is an illustration of a polishing pad contacting a seriesof small heated rollers that are spaced across the surface of thepolishing pad.

[0011]FIG. 3 is an illustration of a polishing pad contacting a heatedpin board having a plurality of raised pins mounted onto the board.

[0012]FIGS. 4A, 4B, 4C, and 4D are top views of patterns of a thermalmask to be placed in contact with the surface of a polishing pad to forma patterned portion: semi-circular lines (FIG. 4A), isolated regions(FIG. 4B), XY crosshatch (FIG. 4C), and spiral (FIG. 4D).

DETAILED DESCRIPTION OF THE INVENTION

[0013] The invention is directed to a polishing pad comprising sinteredparticles of a thermoplastic resin. A surface of the polishing pad isintended to contact a substrate to be polished (i.e., the polishingsurface) and comprises a non-patterned portion with a substantiallyuniform density and a patterned portion with one or more densities thatdiffer from the density of the non-patterned portion.

[0014] The polishing surface of the polishing pad comprises patternedfeatures, which make up the patterned portion of the polishing surface.The features can be, for example, XY crosshatch, spirals, concentricrings, a plurality of isolated regions (e.g., dots or polyhedrons),semi-circular lines, or straight lines. The patterned portion of thepolishing surface typically comprises one or more of the features. Thepatterned features, and thus the patterned portion of the polishingsurface, can be uniformly distributed (e.g., symmetrically orsystematically distributed) over the polishing surface of the polishingpad or can be randomly distributed (e.g., asymmetrically ornon-systematically distributed) over the polishing surface of thepolishing pad. For example, the patterned feature may be a randomlydistributed pattern that is substantially repeated spatially from pad topad. The location of the patterned portion with respect to the center ofthe polishing surface of the polishing pad is flexible. The patternedportion may be localized over the center of the polishing surface or maybe localized over the periphery of the polishing surface. Typically, thepatterned portion of the polishing pad comprises, consists essentiallyof, or consists of a pattern feature having a minimum dimension (e.g.,pattern width) of about 1 mm or more. Preferably, the patterned featurehas a minimum dimension of about 2 mm or more (e.g., about 3 mm ormore).

[0015] The surface of the polishing pad that is not included in thepatterned portion described above is referred to as the non-patternedportion. The non-patterned portion and patterned portion of thepolishing pad each have a surface area on the polishing surface. Theratio of the surface area for the non-patterned portion to the surfacearea of the patterned portion typically is about 95:5 to about 5:95.Preferably, the ratio is about 95:5 to about 50:50. More preferably, theratio is about 90:10 to about 70:30.

[0016] The non-patterned portion of the polishing pad has a differentdensity than the patterned portion of the polishing pad. The density ofthe non-patterned and patterned portions of the polishing pad ismeasured over a polishing pad volume defined in the x and y directionsby the patterned or the non-patterned portion of the polishing surface,and in the z direction by the thickness of the polishing pad (i.e., thedimension which connects the polishing surface of the polishing pad andthe bottom surface of the polishing pad), particularly the thickness ofthe patterned features of the polishing pad that becomes exposed or isworn away during the lifetime of the polishing pad. The lifetime of thepolishing pad may be indicated by a decrease in polishing performancecharacteristics, e.g., by a degradation in polishing uniformity, or byreaching the end of the groove depth (if grooved features are formed onthe surface of the polishing pad). Typically the amount of the polishingpad exposed during the polishing pad lifetime is about 10% or more(e.g., about 20% or more) of the total polishing pad thickness. Moretypically, the amount of the polishing pad exposed during the lifetimeof the polishing pad is about 30% or more (e.g., about 40% or more) ofthe total polishing pad thickness. The amount of the polishing padexposed during the polishing pad lifetime generally is about 90% or less(e.g., about 60% or less).

[0017] Typically, the non-patterned portion of the polishing pad has asubstantially uniform density throughout. The patterned portion of thepolishing pad typically has one density or more than one density (i.e.,multiple different densities) throughout the portion, with at least onesuch density, and optimally all such densities, differing from thedensity of the non-patterned portion. Typically, the density of thenon-patterned portion is about 0.1 g/cm³ or higher (e.g., about 0.2μg/cm³ to about 1.1 g/cm³). Preferably, the non-patterned portion has adensity of about 0.5 g/cm³ to about 0.95 g/cm³. The patterned portionpreferably has a higher density than the non-patterned portion of thepolishing pad. For example, the patterned portion typically has adensity of about 0.5 g/cm³ or higher, preferably about 0.7 g/cm³ orhigher, and more preferably about 0.9 g/cm³ or higher. Preferably, thepatterned portion has a density that is about 0.08 g/cm³ to about 0.5g/cm³ higher (e.g., about 0.1 g/cm³ to about 0.2 g/cm³ higher) than thedensity of the non-patterned portion.

[0018] The polishing pad typically has a void volume (e.g., porosity)and is therefore not a solid polishing pad. The patterned portion of thepolishing pad preferably has a different void volume than thenon-patterned portion of the polishing pad. The void volume of thepatterned and non-patterned portions is measured using the same totalpolishing pad volume described above with respect to the density of thepatterned and non-patterned portions. The non-patterned portiontypically has a higher void volume than the patterned portion of thepolishing pad. Preferably, the non-patterned portion of the polishingpad has a void volume of about 10% or more (e.g., about 20% or more orabout 30% or more). More preferably, the patterned portion of thepolishing pad has a void volume of about 5% to about 30%.

[0019] The polishing pad comprises particles of thermoplastic resin. Thethermoplastic resin typically is selected from the group consisting ofpolyvinylchloride, polyvinylfluoride, nylon, fluorocarbon,polycarbonate, polyester, polyacrylate, polymethacrylate, polyether,polyethylene, polyamide, polyurethane, polypropylene, and copolymers andmixtures thereof. Preferably, the thermoplastic resin is a urethaneresin.

[0020] The non-patterned portion and/or the patterned portion of thepolishing pad optionally further comprise grooves on the polishingsurface. Such grooves can be in any suitable pattern and can have anysuitable depth and width. The polishing pad can have two or moredifferent groove patterns, for example a combination of large groovesand small grooves. Preferably, the polishing pad at least comprisessmall grooves produced by standard pad conditioning methods. In oneembodiment, for a polishing pad having a patterned portion comprisinglines of density, the grooves are oriented perpendicular to the lines ofdensity.

[0021] The non-patterned portion and/or the patterned portion of thepolishing pad optionally further comprise one or more apertures ortranslucent regions (e.g., windows). The inclusion of such apertures ortranslucent regions is desirable when the polishing pad is to be used inconjunction with an in situ CMP process monitoring technique. Theaperture can have any suitable shape and may be used in combination withdrainage channels for eliminating excess polishing composition on thepolishing surface. The translucent region or window can be any suitablewindow, many of which are known in the art. For example, the translucentregion can comprise a glass or polymer-based plug that is inserted in anaperture of the polishing pad or may comprise the same polymericmaterial used in the remainder of the polishing pad.

[0022] The polishing pad of the invention desirably is produced by (i)providing a polishing pad with a first density comprising particles of athermoplastic resin, (ii) heating a portion of the polishing pad tocause the thermoplastic resin particles to flow, and (iii) cooling thepolishing pad, thereby causing the flowed thermoplastic resin particlesto solidify with a second density that is higher than the first densityand forming a polishing pad having a non-patterned portion with thefirst density and a patterned portion with one or more densities thatdiffer form the density of the non-patterned portion.

[0023] The polishing pad, prior to the heating step, has a first densitycorresponding to the density of the polishing pad obtained aftersintering particles of the thermoplastic resin. The thermoplastic resinparticles can be any of the thermoplastic resin particles describedabove. The polishing pad, prior to the heating step, has a substantiallyuniform density throughout the polishing pad. The first densitycorresponds to the density of the non-patterned portion described above.

[0024] One or more portions of the polishing pad having the firstdensity are then heated such that the thermoplastic resin particlesbegin to flow. In the portions of the polishing pad where thethermoplastic resin particles flow, the density will change such thatthose portions have a second density that is higher than the firstdensity of the polishing pad.

[0025] One or more portions of the polishing pad can be heated by avariety of techniques so as to produce a patterned polishing pad withportions of different density. Preferably, the method of heating doesnot involve the use of high pressure or stress, which can damage thepolishing pad. For example, a portion of the polishing pad can be heatedby contacting the polishing pad with one or more patterned rollers asdepicted in FIG. 1 and FIG. 2. In FIG. 1, a polishing pad (10) of afirst density has a polishing surface (11) that is contacted with apatterned roller (12), which consists of heated pins (14), or otherraised, shaped features, mounted onto a cylinder (16). The resultingpolishing pad (17) has a patterned portion consisting of spaced regions(18) that are areas of a second, higher density, and a non-patternedportion (19) that retains the first density. In FIG. 2, a polishing pad(20) has a polishing surface (21) that is contacted with multiplerollers (24) that are spaced apart relative to the surface of thepolishing pad. The resulting polishing pad (27) has a patterned portion(28) consisting of separated lines of the second, higher density, and anon-patterned portion (29) that retains the first density.Alternatively, a portion of the polishing pad can be heated bycontacting a polishing pad with a heated pin board as depicted in FIG.3. In FIG. 3, a polishing pad (30) has a polishing surface (31) that iscontacted with a pin board (32), which consists of heated pins (34), orother raised, shaped features, mounted onto a board (36). The resultingpolishing pad (37) has a patterned portion consisting of spaced regions(38) that are areas of a second, higher density, and a non-patternedportion (39) that retains the first density. A portion of the polishingpad also can be heated by contacting the polishing pad with a patternedmask in the presence of an external heat or radiation source. Examplesof suitable external heat or radiation sources include jets of hot air,lasers, microwave radiation, or ultraviolet radiation. The patternedmask can have one or more of the pattern designs described aboveincluding semi-circular lines, a plurality of isolated regions, XYcrosshatch, spirals, as depicted in FIGS. 4A-4D, respectively, or otherpatterns such as concentric rings and straight lines.

[0026] After heating one or more portions of the polishing pad, thepolishing pad is cooled such that the heated portions of the polishingpad solidify to the second density. The resulting polishing pad has anon-patterned portion, which retains the first density and a patternedportion, which has a second density. The second density will bedifferent from and higher than the first density. The patterned portionof the polishing pad can have two or more second densities that aredifferent from the first density. Typically, the two or more seconddensities will be part of a continuum of increasing density.

[0027] The polishing pad of the invention is particularly suited for usein conjunction with a chemical-mechanical polishing (CMP) apparatus.Typically, the apparatus comprises a platen that rotates, a polishingpad of the invention in contact with the platen and rotating with theplaten, and a carrier that holds a substrate to be polished bycontacting the surface of the polishing pad intended to contact asubstrate to be polished. The polishing of the substrate takes place bythe substrate being placed in contact with the polishing pad and thenthe polishing pad moving relative to the substrate, typically with apolishing composition therebetween, so as to abrade at least a portionof the substrate to polish the substrate. The CMP apparatus can be anysuitable CMP apparatus, many of which are known in the art. Thepolishing pad of the invention also can be used with linear polishingtools.

[0028] The polishing pad described herein is suitable for use inpolishing many types of substrates and substrate materials. For example,the polishing pad can be used to polish a variety of substratesincluding memory disks, semiconductor wafers, field emission displays,and other microelectronic substrates, especially substrates comprisinginsulating layers (e.g., oxide, nitride, or low dielectric materials),and/or metal-containing layers (e.g., copper, tantalum, tungsten,aluminum, nickel, titanium, platinum, ruthenium, rhodium, iridium orother noble metals).

[0029] All references, including publications, patent applications, andpatents, cited herein are hereby incorporated by reference to the sameextent as if each reference were individually and specifically indicatedto be incorporated by reference and were set forth in its entiretyherein.

[0030] The use of the terms “a” and “an” and “the” and similar referentsin the context of describing the invention (especially in the context ofthe following claims) are to be construed to cover both the singular andthe plural, unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. Recitation of ranges of valuesherein are merely intended to serve as a shorthand method of referringindividually to each separate value falling within the range, unlessotherwise indicated herein, and each separate value is incorporated intothe specification as if it were individually recited herein. All methodsdescribed herein can be performed in any suitable order unless otherwiseindicated herein or otherwise clearly contradicted by context. The useof any and all examples, or exemplary language (e.g., “such as”)provided herein, is intended merely to better illuminate the inventionand does not pose a limitation on the scope of the invention unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe invention.

[0031] Preferred embodiments of this invention are described herein,including the best mode known to the inventors for carrying out theinvention. Variations of those preferred embodiments may become apparentto those of ordinary skill in the art upon reading the foregoingdescription. The inventors expect skilled artisans to employ suchvariations as appropriate, and the inventors intend for the invention tobe practiced otherwise than as specifically described herein.Accordingly, this invention includes all modifications and equivalentsof the subject matter recited in the claims appended hereto as permittedby applicable law. Moreover, any combination of the above-describedelements in all possible variations thereof is encompassed by theinvention unless otherwise indicated herein or otherwise clearlycontradicted by context.

What is claimed is:
 1. A polishing pad comprising sintered particles ofa thermoplastic resin, wherein a surface of the polishing pad intendedto contact a substrate to be polished comprises a non-patterned portionwith a substantially uniform density and a patterned portion with one ormore densities that differ from the density of the non-patternedportion.
 2. The polishing pad of claim 1, wherein the patterned portionis uniformly distributed on the surface of the polishing pad.
 3. Thepolishing pad of claim 1, wherein the patterned portion is randomlydistributed on the surface of the polishing pad.
 4. The polishing pad ofclaim 1, wherein the patterned portion comprises one or more featuresselected from the group consisting of XY crosshatch, spirals, concentricrings, a plurality of isolated regions, semi-circular lines, andstraight lines.
 5. The polishing pad of claim 1, wherein thenon-patterned portion has a density of about 0.2 g/cm³ to about 1.1g/cm³.
 6. The polishing pad of claim 1, wherein the patterned portionhas at least one density of about 0.5 g/cm³ or higher.
 7. The polishingpad of claim 5, wherein the patterned portion has a density that isabout 0.1 to about 0.2 g/cm³ higher than the density of thenon-patterned portion.
 8. The polishing pad of claim 1, wherein theratio of surface area of the patterned portion to non-patterned portionis about 95:5 to about 50:50.
 9. The polishing pad of claim 1, whereinthe patterned portion comprises patterned features having a minimumdimension of about 2 mm or more.
 10. The polishing pad of claim 1,wherein the thermoplastic resin is selected from the group consisting ofpolyvinylchloride, polyvinylfluoride, nylon, fluorocarbon,polycarbonate, polyester, polyacrylate, polymethacrylate, polyether,polyethylene, polyamide, polyurethane, polypropylene, and copolymers andmixtures thereof.
 11. The polishing pad of claim 9, wherein thethermoplastic resin is a urethane resin.
 12. The polishing pad of claim1, wherein the patterned portion has at least one density that is higherthan the non-patterned portion of the polishing pad.
 13. The polishingpad of claim 1, wherein the patterned portion has a lower void volumethan the non-patterned portion of the polishing pad.
 14. The polishingpad of claim 1, the patterned portion further comprises one or morefeatures selected from the group consisting of grooves and translucentwindow regions.
 15. A method for producing a polishing pad comprising:(a) providing a polishing pad with a first density comprising particlesof a thermoplastic resin, (b) heating a portion of the polishing pad tocause the thermoplastic resin particles to flow, and (c) cooling thepolishing pad, thereby causing the flowed thermoplastic resin particlesto solidify with a second density that is higher than the first densityand forming a polishing pad having a non-patterned portion with thefirst density and a patterned portion with one or more densities thatdiffer from the density of the non-patterned portion.
 16. The method ofclaim 15, wherein the thermoplastic resin is selected from the groupconsisting of polyvinylchloride, polyvinylfluoride, nylon, fluorocarbon,polycarbonate, polyester, polyacrylate, polymethacrylate, polyether,polyethylene, polyamide, polyurethane, polypropylene, and copolymers andmixtures thereof.
 17. The method of claim 15, wherein the thermoplasticresin is a urethane resin.
 18. The method of claim 15, wherein a portionof the polishing pad is heated by contacting the polishing pad with oneor more patterned rollers.
 19. The method of claim 18, wherein thepatterned rollers comprise raised features mounted onto a cylinder. 20.The method of claim 15, wherein a portion of the polishing pad is heatedby contacting the polishing pad with a pin board.
 21. The method ofclaim 15, wherein a portion of the polishing pad is heated by contactingthe polishing pad with a patterned mask in the presence of an externalheat or radiation source.
 22. The method of claim 15, wherein a portionof the polishing pad is heated by contacting the polishing pad with jetsof hot air.
 23. A chemical-mechanical polishing apparatus comprising:(a) a platen that rotates, (b) a polishing pad of claim 1, wherein thepolishing pad is in contact with the platen and rotates with the platen,and (c) a carrier that holds a substrate to be polished by contactingthe surface of the polishing pad intended to contact a substrate to bepolished.
 24. A method of polishing comprising: (a) contacting asubstrate with the polishing pad of claim 1 and a polishing composition,(b) moving the substrate relative to the polishing pad to abrade atleast a portion of the substrate to polish the substrate.
 25. The methodof claim 24, wherein the substrate comprises an insulating layerselected from silicon dioxide, silicon nitride, and a dielectricmaterial having a dielectric constant of about 3.5 or lower.
 26. Themethod of claim 24, wherein the substrate comprises a metal-containinglayer comprising copper, tantalum, tungsten, aluminum, nickel, titanium,platinum, ruthenium, rhodium, or iridium.
 27. The method of claim 24,wherein the polishing composition comprises an abrasive, a liquidcarrier, and optionally an oxidizer or complexing agent.